The present invention relates primarily to methods use in site-rehabilitation efforts of ground water and/or soil contaminated with organic compounds such as hydrocarbon constituents associated with diesel fuel, gasoline, kerosene, solvents and creosote.
At the present time, site remediation for hydrocarbon constituents takes years and decades. The most widely used aquifer remediation technology is known as "pump and treat". This consists of extracting (pumping) groundwater from recovery well(s), and pumping it to an above-ground treatment system, removing the contaminants from the extracted groundwater, and re-infiltrating the now uncontaminated groundwater back to the aquifer or discharging to a surface water body. This method has had an extremely poor success rate and is now projected by the EPA to take 30 years of operation per site to achieve target levels. This method also has proven to be inefficient and not cost effective. Due to the contaminated soil matrix below the water table, the diffusion of contaminants from the soil matrix to the groundwater continuously re-contaminates the groundwater, thereby resulting in site rehabilitation efforts to be measured in decades. The pump and treat method's cleanup times are dependent on aquifer permeability, and on natural diffusion rates from the soil matrix to the pore water, and this method does not address the soil contamination above the water table. Remediation stress on the contaminated area dissipates drastically with distance from the recovery well.
Another popular method, often used separately or in conjunction with "pump and treat", is soil vacuum extraction. This method consists of extracting subsurface vapors from the soil above the water table via a vacuum pump. However, this extraction step has little or no effect on remediating any associated groundwater. Further, it is dependent on the natural soil diffusion rates for releasing contaminants from the soil to the air in the pore space. Remediation stress dissipates drastically with distance from the vapor extraction point.
In-situ biodegradation of soil and groundwater is a remediation technique that has gained attention but has had little or no success in achieving cleanup target standards. This method is a "livestock nurturing" approach that introduces bacteria (micro-organisms) or enhances the naturally occurring bacteria to eat or break down the contaminants. For in-situ conditions, this is a very slow process and has had little or no success in achieving normal regulatory cleanup target levels, particularly in the microgram-per-liter or parts-per-billion range. It is also questionable as to how much remediation stress this method applies to the contaminated area, particularly after the initial contaminant concentration reduction.
Because the pump and treat, soil vacuum extraction, and in-situ biodegradation methods are extremely slow processes that depend on subsurface conditions or yields, and require years of implementation at the site, they can be considered as "passive" remediation methods. These methods apply their maximum remediation stress to small, selected portions of the contaminated area, and little or no remediation stress to the larger percentage of the contaminated area. Furthermore, the amount of remediation stress these methods put on their selected areas is well below the level of remediation stress or intensity produced by our invention.
A known "active" remediation process is soil excavation. Although this process is successful on soil above the water table, it has significant remediation limitations on soil or groundwater in the underlying aquifer. If soil below the water table is removed, remaining contaminated groundwater in the aquifer will re-contaminate the backfill below the water table, thereby resulting in the creation of additional contaminated soil.
The published prior art does not present efficient and effective methods to achieve typical Federal and State site restoration standards in a short period of time, particularly when contaminated groundwater is involved.
For example, U.S. Pat. No. 5,221,159 (Billings et al) requires vacuum extraction in conjunction with oxygenated air injection, plus natural and enhanced biodegradation. This patent specifically indicates a reliance solely on biodegradation to address diesel constituents, and also specifically states that site remediation time is measured in terms of years, thereby indicating that maximum remediation stress is not achieved. U.S. Pat. No. 5,277,518 (Billings et al), a continuation-in-part, discloses a venting/collection system for air emissions, and requires a vent well within 200 feet on an air entry point. Both of these patents can be considered as being directed to passive techniques.
U.S. Pat. No. 4,435,292 (Kirk) requires simultaneous air injection and evacuation in a closed loop system for mass transfer of the contaminants to the carrier gas. Extraction via negative pressure (vacuum points) is critical to this method.
U.S. Pat. No. 4,842,448 (Koerner) uses gas injection and its forced extraction from the soil, but requires impermeable horizontal and vertical barriers around the contaminated area. This method is based on pressure reduction (vacuum) to draw out the carrier gas.
U.S. Pat. No. 4,832,122 (Corey et al) uses in-situ gas injection and vacuum extraction to address volatile contaminants in groundwater. This method requires significant negative pressure/vacuum to draw the injected gas across the contaminated groundwater. U.S Pat. No. 5,263,795 (Corey et al) is somewhat of an extension of the '122 patent but addresses metal contamination, relies on bio-degradation, and treats contaminants in-situ without removal.
U.S. Pat. No. 5,076,727 (Johnson et al) describes a closed loop system of injection and vacuum withdrawal, designed to heat the soil with microwaves, thereby causing release of nonvolatile hydrocarbon contaminants. The patent states that negative pressure (vacuum) is needed to withdraw the vapors, and requires an impermeable surface. U.S. Pat. No. 5,193,934 (Johnson et al) also describes a process designed to heat the soil and vaporize the hydrocarbons, but this version inserts hot combustion products into soil under negative pressure conditions in a closed loop system with an impermeable surface.
U.S. Pat. No. 5,032,042 (Shuring et al) describes a fracturing technique to establish preferential flow channels targeting the soil above the water table to enhance vacuum extraction or air injection.
U.S. Pat. No. 5,249,888 (Braithwaite) relies on creating negative pressure (vacuum) in the subsurface and does not require air injection.
U.S. Pat. No. 5,246,309 (Hobby) discloses a closed loop system that relies on negative subsurface pressure to draw and recirculate vapors through the contaminated area. The contaminants in the vapors are treated by the biodegradation effects from micro-organisms in the subsurface and a surface bio-reactor.
U.S. Pat. No. 5,251,700 (Nelson) is a method and device for injecting hot gas under an impermeable surface and into the subsurface using specially adapted wellbore outlets that orient the hot vapor, injected into the soil from a well bore, in a pre-determined or controlled well bore exiting pattern. This method requires dewatering or removal of free flowing water in the soil area or volume of soil prior to remediation.